A. Field of the Invention
The present invention relates to tools for computerized process modelling and project planning.
B. Related Art
Application programs for project planning have conventionally implemented one of several classical analytical network techniques. An example of one such technique is the Critical Path Method (CPM). In project management tools using the Critical Path Method, the evolution of time in each project is defined in advance. In such systems, every activity and every event of each project occurs only once during a single project execution. Thus, in such systems it is not possible to return to repeat an activity that has already been carried out. This inability to repeat an activity is a shortcoming in that there are many instances in actual projects where activities need to be repeated. Further, there are instances where the recurrence of an activity will need to be modified based on feedback from a prior occurrence of a logically subsequent activity. For example, a part manufactured during a first activity may need to be re-manufactured or repaired based on the results of a subsequent inspection.
An improved analytical network technique known as GERT (Graphical Evaluation and Review Technique) is described in an article entitled "Temporal Analysis, Cost Minimization, and the Scheduling of Projects with Stochastic Evolution Structure (L. Foulds and K. Neumann, Asia-Pacific Journal of Operational Research 6 (1989) pp. 167-191). GERT fills many of the shortcomings of CPM in that it includes provisions for handling the recurrence of activities and feedback.
While GERT is an improvement relative to CPM, a number of problem areas remain. For example, typical project planning applications based on CPM or GERT do not have the capability of utilizing only N of M defined predecessors or successors to an activity's start or finish, where N is greater than 1 but less than M. Nor can a case where N equals zero be handled by either. For example, if five successors are defined to an activity's finish, one cannot activate only four of the five if one uses either CPM or GERT.
Another deficiency with both conventional CPM and GERT applications is the inability to handle variations in activity duration based on available types and quantities of resources. Conventional project planning tools provide the capability to specify a minimum number and type of resources required to perform an activity. For example, an activity may require engineers. Engineers may come in two types, veteran and novice. In conventional project planning tools, one may specify some minimum quantity and type of resources that are required to perform the task. Perhaps the task can be performed by either five veteran engineers or five veterans and two novices, or four veterans and four novices.
While the above-described system accounts for the possibility that different types of resources may be satisfactory to perform a task, the decision is binary. In other words, it assumes either a go or a no go condition. It does not take into account that in the real world, other types or combinations of resources may be able to accomplish a task, albeit in a degraded or perhaps upgraded mode. For example, if there are five veteran engineers available to an activity, it may be completed in duration X. If, however, only four veteran engineers are available, then two additional novice engineers may be required to keep the duration at X. Alternatively, however, if only four veterans and one novice are available the duration of the activity may increase to X+1. If only two veterans are available, the duration may increase to X+20.
Thus, what is needed is a flexible project/process modelling tool that takes into account the possibility that an activity's duration may vary from pass to pass based on types of available resources, and that such duration can vary due to other factors such as the point in time within a project or process.